1. Field of the Invention
This invention relates to the manufacture of containers from foil. The invention relates in particular to a method of and apparatus for manufacturing containers from foil and to novel containers which have been manufactured with the apparatus and in accordance with the method.
2. Description of the Prior Art
In the manufacture of containers from foil the cost of material is the predominant cost factor, so that thin foil is used, which, while it is flat and smooth on the base of the container, becomes wrinkled on the walls. While the art of producing drawn metal sheels has been widely used and highly developed, the problem of eliminating wrinkles in the sides and flanges of the finished shell has never been satisfactorily solved in respect to many forms of shells and in respect to many kinds of and thicknesses of metal.
According to conventional drawing practice the sheet metal blank is put in position across a die cavity and is held in place against the die face by a yielding blank holder or pressure pad through which a punch is moved to engage the sheet and force the same into the die cavity, and as the punch enters the die, the border portion of the blank, that is held by yielding clamping pressure between the die face and the pressure pad, is drawn inwardly toward the drawing edge, as for example in the formation of a circular shell, or at the rounded corners of a rectangular shell, there must be a progressive reduction in the circumferential dimension of the diverging portions of the flange as they approach the drawing edge. In other words, each segmented portion of the border must become narrower as it approaches or is drawn inwardly toward the drawing edge, and this produces what may be termed circumferentially acting compressive forces in such border which tend to produce radially extending waves or wrinkles in the border portion of the blank. Although they have sometimes been described as pleats, the wrinkles formed in the conventional technique are in fact the result of random crumpling of the foil between die parts. The deeper the container to be formed, the more the wrinkles are formed and enlarge, and the greater are the problems arising from the wrinkles. The wrinkles cause stress in the foil which places limitations on the thinness of foil that can be used, the depth of container that can be formed and the appearance of the resulting product.